Vista is the biggest revision to Windows in over a decade. It will be a major change, not only for consumer and corporate Windows users, but for computer makers, software creators and many others downstream.

But what’s in Vista? How will it be sold? And what kind of computer will be needed to run it? Here’s a rough guide to the new Leviathan of the digital seas.

WHY VISTA?

Even after a major overhaul a couple of years back, Windows XP is a security nightmare. With Vista, Microsoft claims to have built in better security from the start, reducing — though not eliminating — the need to buy, learn and maintain add-on security software. The company says better security is Vista’s biggest advantage.

For instance, with the new program you’ll have to type in your administrator ID and password before installing software, to stop malicious software from installing itself silently. And Vista will have built-in parental controls.

Vista’s next big feature is built-in desktop search. Think of this as the Google Desktop search on steroids. From any screen, you’ll be able to start typing a search term and Vista will comb your hard disk for every document, photo, email, song and video that meets that criterion. It should be much faster and better than add-on search programs.

In addition, you’ll be able to save searches in “virtual folders,” which will automatically continue to collect files that meet your search specifications. So if you save a search for “Fountains of Wayne” as a virtual folder and check it a month later, it will contain every e-mail that mentioned the pop band as well as any photos you took at their concert and new songs by the band that you downloaded — even though none of these things existed when you first did the search.

The last major new feature is a rich new user interface. Called Aero, it includes a powerful new graphics system that enables such new extras as transparent windows, animation of certain screen elements (similar to the “funnel” effect Mac users are familiar with when closing a file) and the ability to see reduced, live views of all your running programs at once.

There are lots of smaller changes as well. For instance, there’s a dashboard with small programs (calendar, weather updates and stock tickers, among others) that run quickly, called Gadgets. There’s also new music and video player software; a new built-in Web browser with tabbed browsing; a new, free email program with junk-mail filtering; and a new photo-organizing program.

Many of these features are already available on the Apple Macintosh — some have been for years — but they will seem fresh to most Windows users.

HOW WILL YOU BUY IT?

Like past versions of Windows, Vista will be sold in two ways: The vast majority of people will get it by buying a new PC with Vista preloaded at the factory. That way, they’ll know the hardware and software are compatible. And a small percentage of people, either brave souls or those with PCs too new to replace, will buy Vista in a box and upgrade their computers manually.

Either way, Vista won’t be simple to purchase. That’s because it will come in at least five different flavors, compared with two versions when Windows XP launched in 2001. There will be two consumer versions of Vista, two business versions and one version that includes everything, called “Ultimate.” Also, two current special editions of Windows, the Tablet and Media Center versions, will be folded into some, but not all, of the five Vista editions.

For consumers, the biggest issue will be choosing between the Home Basic and Home Premium versions of Vista, either on new machines or in boxes. Home Premium will include the new Aero user interface along with all the security, search and other features described above. It will also have updated versions of the features currently included in the Media Center and Tablet editions of Windows XP. But Home Premium won’t run on most Windows PCs currently in the hands of consumers, and it also won’t run on new, low-end PCs. That’s because it requires hefty hardware to work right.

Most current PCs, and all the bargain-priced new ones preloaded with Vista next January, will be able to run only Home Basic, which is a stripped-down version of Vista. Microsoft insists that Home Basic will have the same security system and search features as Premium, but it won’t include the new Aero user interface and will probably lack some other features. In essence Home Basic will look and feel like a modestly improved version of Windows XP, even though Microsoft says there’ll be major improvements under the covers.

Power users, and those who want every option just in case, may go for the Ultimate version of Vista. It not only will roll up everything in the consumer and business versions, it may also have some added bells and whistles. Microsoft hasn’t announced prices yet.

WHAT HARDWARE WILL YOU NEED?

The stripped-down version of Vista, Home Basic, will run on fairly routine PCs, albeit ones with plenty of memory.

The Premium and Ultimate versions will likely require at least a midrange model or a high-end configuration.

Microsoft hasn’t officially released the recommended hardware specs. But I expect the company to recommend 512 megabytes of memory for Home Basic and a gigabyte of memory for Premium. Based on past experience, I advise doubling those amounts, to a gigabyte of memory for Basic and 2 gigabytes for Premium.

Another crucial hardware factor will be the computer’s video system. Basic Vista can run on any graphics hardware that creates a screen resolution of at least 800×600. That covers most bargain computers with graphics chips that are integrated with the machine’s motherboard and which share main memory. But Premium and Ultimate will run best on machines with a full-blown graphics card and dedicated video memory of at least 128 megabytes.

You will be able to run Home Basic on the slowest processors available, but for the better versions of Vista, you’ll need a processor running at a speed of at least 1 gigahertz. I would opt for as fast a processor as you can afford and for one with two “cores” rather than one. (A dual-core processor is essentially like having two processors on one chip.)

Vista will also support so-called 64-bit processors, which can gulp down more information than current machines. But I wouldn’t worry about that for now, unless you’re a power user. There’s very little 64-bit software available for consumers.

Vista may not be something to leap into right away. You may want to wait a while to see about defects and, especially, to see if it seems more secure, as promised.

This year, however, Microsoft will up the ante with a new version of Windows called Vista. Due in the fall, in time for holiday computer shopping, Vista is an effort to make Windows truly secure from the ground up, while also making it easier to use and pretty enough to rival Apple’s current version of OS X, Tiger. (Apple is planning yet another new edition, called Leopard, due around the same time.)

Vista will be the most dramatic upgrade to Windows in more than a decade. But there will be a price for Vista’s improvements — most current PCs won’t be able to take advantage of all its features. To get full use out of the new system, you will very likely need to upgrade or replace your current computer. Vista will adapt to older or less powerful machines by disabling some of its features, but that’s likely to be unsatisfying for many users. Also, as of this writing, Microsoft is planning to sell Vista in as many as seven different configurations for different types of users. That will be not only confusing, but if you select the more capable configurations, probably expensive, too. (Microsoft hasn’t released pricing yet.)

So here’s a preliminary look at Vista’s major new features, as well as some guidance on hardware. Microsoft’s mantra for Vista is “Confident, Clear and Connected.” By “Confident,” the company means that it promises to clean up the security mess that has been the main headache for users of Windows. Microsoft says Vista will be much harder to hack into, and much less prone to viruses and spyware, than today’s Windows. For instance, Vista users will be asked for their user name and password anytime software is being installed –designed to prevent the surreptitious software installations that plant spy-ware on a PC. And Vista will have built-in systemwide parental controls, so you can limit what your child can see and do on the computer. Both features are already built into Apple’s Tiger and work well, so if they are executed properly on Vista, they should be a boon.

By “Clear,” Microsoft is referring to new ways of finding and visualizing your files. Vista will have rapid, modern, built-in desktop searching. And it will have something called “virtual folders” that capture all files meeting certain criteria you can set, no matter where you store them. For instance, you could set up a virtual folder to show all files and e-mails mentioning a certain person or topic. Again, both features are already in Apple’s operating system, where they have proved popular. Some editions of Vista will also incorporate the features of today’s Windows Media Center edition, including the ability to play and record TV programs.

The “Connected” promise from Microsoft includes a centralized synchronization feature, like the one already present on the Mac, that can keep data in sync on cell phones and PDAs. Vista will also look dramatically better — and more like Mac software — with 3D icons, transparent windows and tiny previews of file contents.

So what kind of hardware will you need for all this? Well, Vista won’t work well with the processors sold in today’s budget PCs. I suggest you consider a new computer with at least a midrange processor, and preferably a so-called dual-core processor, which packs two brains into its innards, though a single-core model will do. You might even look for a processor capable of handling future software called “64-bit,” though it’s not absolutely necessary.

Memory will also be crucial for Vista. I expect Microsoft to recommend 512 megabytes, but since the company tends to understate memory requirements, I suggest a full gigabyte, far more than what’s on the average PC today. You’ll also need a bigger hard disk, especially if you want to use the new TV-recording capabilities that will be built into some editions of Vista. I suggest at least 160 gigabytes. Luckily, large hard disks are now pretty inexpensive.

Likewise, video capability will be key to utilizing Vista’s new visual effects. Today’s PCs often use integrated graphics chips, which are pretty basic and drain memory. That won’t cut it for Vista, at least until integrated graphics chips are beefed up next fall. If you seek a Vista-capable machine before then, look for one with a separate graphics card with its own dedicated memory, preferably 128 megabytes, though 64 will do.

Vista will boost DVD recording — it will support the new, high-definition DVDs currently in development and make it easier to burn DVDs for both multimedia and file backup. You’ll need a high-end DVD-recording drive to reap the rewards.

I can’t say how good Vista will be until I test and review the final, or near final, product, in late summer. But from the demos I’ve seen, Vista has great promise — if you have the right hardware.

There have long been computer viruses, but until the past couple of years, they were mainly a nuisance. Now they have grown into a serious problem — by one account there were 5,000 new Windows viruses discovered in the first six months of 2004. And the virus plague has been trumped by a new type of malicious software, spyware, which can track your activities, bombard you with unwanted ads, even steal your identity.

Spam has also grown exponentially, clogging e-mail boxes and carrying with it malicious software. For some people, e-mail has become a curse.

And that’s not all. Every minute of every day, hackers using automated software scan the Internet looking for computers vulnerable enough to invade and, in some cases, to surreptitiously take over. Without your knowledge, they can turn your computer into a “zombie” machine rigged to help them spread their nasty viruses, spam and spyware.

So for consumers and small businesses — everyone without a large IT department to manage security — the Windows computers they use have become huge burdens instead of helpful tools. If you do get a severe virus or spyware infestation, you may have to spend hundreds of dollars and many hours to wipe your hard disk clean and start fresh, quite possibly losing crucial data in the process.

And prevention is almost as painful as the disease, because the computer industry has so far come up with only half-baked and piecemeal solutions to these threats. You have to watch every move you make online and install a bunch of security programs, which require monitoring, constant updating and, often, annual fees.

Each of these security programs deals only with a narrow slice of the problem. Firewalls can keep out invaders, but they don’t stop viruses, spyware or spam. Antivirus programs don’t catch most spyware. Antispyware programs don’t stop viruses. And neither stops spam. For that, you need anti-spam software, which does nothing about viruses or spyware that invade your system through avenues other than spam.

You can buy “suites” that combine all these programs, but they are really just bundles of separate applications of widely varying quality stuffed into the same box.

It’s as if you needed a separate burglar alarm system, each with its own control panel, password and monthly fee, for every door and window in your home.

What users need is a simple, all-encompassing security service that would deal with all these threats with minimal user involvement. For now, though, you’ll have to do it yourself.

So here’s my quick guide to Windows security measures. Some of the products I recommend below are free, but others cost money. I like free stuff as much as the next guy, but I don’t believe security is an area where price should govern. You don’t want to entrust your computer’s security to some unknown software author, or even to a well-meaning individual or very small outfit that lacks the resources to keep up with the threats.

Download and install all the security fixes Microsoft issues for Windows. If you have Windows XP, set it to automatically fetch and install these patches (you can do this by clicking on the “Automatic Updates” or “Security Center” icons in the Windows control panel). You should also probably install the massive Service Pack 2 revision of Windows XP, which plugs many security holes. But back up your data first. A significant minority of users have reported big problems with SP2.

Stop using Microsoft’s Internet Explorer Web browser, which has become a four-lane highway for malicious invaders. I recommend instead Mozilla Firefox, which is free at www.mozilla.org [http://www.mozilla.org]. I use it all day, every day.

Windows comes with a firewall program, designed to keep out hackers. But in most versions of the operating system, it’s hard to turn on and configure. Even the improved firewall in the new SP2 revision of Windows XP is inferior to several third-party products. I recommend, and use, ZoneAlarm, a free firewall from Zone Labs, available at www.zonelabs.com [http://www.zonelabs.com]. There are some fancy paid versions of ZoneAlarm, which are also fine, but if you want the free one, you’ll have to look hard on the Web page.

Software to stop spyware is still in its infancy, so I suggest keeping two or three anti-spyware programs on hand. Each program will likely find spyware the others miss. But I recommend relying most on the one I use, Webroot’s Spy Sweeper, available at www.webroot.com [http://www.webroot.com]. It costs $30, including a year of updates, and runs all the time to block incoming spyware. To back up Spy Sweeper, go to www.download.com [http://www.download.com] and get two free programs: Ad-Aware, and Spybot Search and Destroy. Use these for manual scanning.

I recommend Norton AntiVirus from Symantec. It costs $50, including a year of updates. But it works well and has a good automatic updating system. I have been receiving many reports of problems with Symantec’s customer service, so I may have to change my recommendation down the road. But for now, I prefer Norton, and I use it myself.

No antispam program I have tested is wholly satisfying, but I suggest one of two. The first is MailFrontier Desktop, available for $30 at www.mailfrontier.com [http://www.mailfrontier.com]. The second is SpamSubtract, from Intermute, available for $20 at www.spamsubtract [http://www.spamsubtract]. com. They are very different, and each has its strengths and weaknesses. I oscillate between the two every six months or so.

Beyond installing, monitoring and updating all this software, you need to be careful online. Don’t open email attachments you don’t expect and that come from strangers. They may contain viruses or spyware. Don’t download software unless you really need it and are 100 percent certain of the author’s trustworthiness. It could be an infection in disguise. Never click on a link in an e-mail purporting to be from a financial institution, even if it’s your own bank and it looks official. It could be a scam to steal your identity.

And if you’re totally fed up with the security crisis but want to continue using your computer for common tasks, consider dumping Windows altogether and switching to Apple’s Macintosh, which uses its own operating system, called OS X. There has never been a successful virus reported on OS X, and there is little or no spyware for the Mac.

In my view, Macs have better hardware, a better operating system and better bundled software than Windows PCs. They are as good as, and often better than, Windows PCs at e-mail and Web surfing; at word processing and other productivity tasks; and at handling digital photos, videos and music. And most popular Windows file types open right up in Mac programs, without the need for any conversion or translation.

Stay safe out there.